linux/arch/x86/mm/mmap.c
Daniel Cashman 9e08f57d68 x86: mm: support ARCH_MMAP_RND_BITS
x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for
64-bit, to generate the random offset for the mmap base address.  This
value represents a compromise between increased ASLR effectiveness and
avoiding address-space fragmentation.  Replace it with a Kconfig option,
which is sensibly bounded, so that platform developers may choose where
to place this compromise.  Keep default values as new minimums.

Signed-off-by: Daniel Cashman <dcashman@google.com>
Cc: Russell King <linux@arm.linux.org.uk>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Mark Salyzyn <salyzyn@android.com>
Cc: Jeff Vander Stoep <jeffv@google.com>
Cc: Nick Kralevich <nnk@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Hector Marco-Gisbert <hecmargi@upv.es>
Cc: Borislav Petkov <bp@suse.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-14 16:00:49 -08:00

136 lines
3.3 KiB
C

/*
* Flexible mmap layout support
*
* Based on code by Ingo Molnar and Andi Kleen, copyrighted
* as follows:
*
* Copyright 2003-2009 Red Hat Inc.
* All Rights Reserved.
* Copyright 2005 Andi Kleen, SUSE Labs.
* Copyright 2007 Jiri Kosina, SUSE Labs.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <linux/personality.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/limits.h>
#include <linux/sched.h>
#include <asm/elf.h>
struct va_alignment __read_mostly va_align = {
.flags = -1,
};
static unsigned long stack_maxrandom_size(void)
{
unsigned long max = 0;
if ((current->flags & PF_RANDOMIZE) &&
!(current->personality & ADDR_NO_RANDOMIZE)) {
max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
}
return max;
}
/*
* Top of mmap area (just below the process stack).
*
* Leave an at least ~128 MB hole with possible stack randomization.
*/
#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
#define MAX_GAP (TASK_SIZE/6*5)
static int mmap_is_legacy(void)
{
if (current->personality & ADDR_COMPAT_LAYOUT)
return 1;
if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
return 1;
return sysctl_legacy_va_layout;
}
unsigned long arch_mmap_rnd(void)
{
unsigned long rnd;
if (mmap_is_ia32())
#ifdef CONFIG_COMPAT
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1);
#else
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
#endif
else
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
return rnd << PAGE_SHIFT;
}
static unsigned long mmap_base(unsigned long rnd)
{
unsigned long gap = rlimit(RLIMIT_STACK);
if (gap < MIN_GAP)
gap = MIN_GAP;
else if (gap > MAX_GAP)
gap = MAX_GAP;
return PAGE_ALIGN(TASK_SIZE - gap - rnd);
}
/*
* Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
* does, but not when emulating X86_32
*/
static unsigned long mmap_legacy_base(unsigned long rnd)
{
if (mmap_is_ia32())
return TASK_UNMAPPED_BASE;
else
return TASK_UNMAPPED_BASE + rnd;
}
/*
* This function, called very early during the creation of a new
* process VM image, sets up which VM layout function to use:
*/
void arch_pick_mmap_layout(struct mm_struct *mm)
{
unsigned long random_factor = 0UL;
if (current->flags & PF_RANDOMIZE)
random_factor = arch_mmap_rnd();
mm->mmap_legacy_base = mmap_legacy_base(random_factor);
if (mmap_is_legacy()) {
mm->mmap_base = mm->mmap_legacy_base;
mm->get_unmapped_area = arch_get_unmapped_area;
} else {
mm->mmap_base = mmap_base(random_factor);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
}
}
const char *arch_vma_name(struct vm_area_struct *vma)
{
if (vma->vm_flags & VM_MPX)
return "[mpx]";
return NULL;
}